Showing papers in "Chronobiology International in 2009"

Shift work and metabolic syndrome: respective impacts of job strain, physical activity, and dietary rhythms.

Abstract: The impact of shift work on cardiovascular disease (CVD) risk factors and metabolic syndrome are not yet completely understood. The objectives of this study were to evaluate the impact of shift work on metabolic syndrome according to two different definitions in a population of strictly rotating shift workers (3x8 h) compared to paired counterparts working only day hours, and to study whether shift work itself is a determinant of metabolic syndrome after taking into account a large panel of confusing factors. We conducted a cross-sectional study comparing 98 strictly rotating shift workers to 100 regular day-workers (all subjects had a long experience of their working rhythms) within the same petrochemical plant. Clinical, behavioral, occupational, and biological data were collected, and a detailed nutritional investigation was done. Shift and day workers were comparable in terms of major CVD factors, and both had a 10 yr Framingham risk scoring of 11%. Shift workers reported an increased job strain and higher total and at-work physical activity. Alterations in metabolic parameters were evident with a rise in triglycerides, free fatty acids, and gamma glutamyl transpeptidase and lower HDL-cholesterol. Multiple logistic regression analysis demonstrated that shift work was associated with occurrence of metabolic syndrome, as defined by the National Cholesterol Education Program-ATPIII criteria, OR: 2.38 (1.13-4.98), but not using the more recent score from the International Diabetes Federation, which gives a major emphasis on abdominal obesity. Total energy intake and contributions of the major nutrients did not differ between the two groups, with the notable exception of saturated lipids (+10% in shift workers). Meal distribution was clearly different: energy intake was more fractionated within the day, with a lesser contribution of breakfast and lunch but with increased intakes during intermediate light meals, particularly in the afternoon and night. Multivariate analyses were performed to test for the influence of dietary rhythms on the development of an NCEP-ATPIII metabolic syndrome. Dietary intakes at breakfast and during intermediate light meals appear to be "protective" against metabolic syndrome, while a high load at dinner favors its occurrence. A high intake at lunch is particularly deleterious to shift workers. However, in all tested models, shift work remained significantly associated with metabolic syndrome, after taking into account potential covariates like job strain, physical activity, quantitative dietary parameters, and meal distribution. A specific follow-up of shift workers should be recommended to occupational physicians.

Global Co‐Distribution of Light at Night (LAN) and Cancers of Prostate, Colon, and Lung in Men

Abstract: The incidence rates of cancers in men differ by countries of the world. We compared the incidence rates of three of the most common cancers (prostate, lung, and colon) in men residing in 164 differ...

The crosstalk between physiology and circadian clock proteins.

Abstract: In mammals, many physiological processes present diurnal variations, and most of these rhythms persist even in absence of environmental timing cues. These endogenous circadian rhythms are generated...

Relationship between Circadian Typology and Big Five Personality Domains

Abstract: We explored the relationship between personality, based on the five‐factor model, and circadian preference. To this end, 503 participants (280 females, 223 males) were administered the Morningness‐...

Persistent Rotating Shift-Work Exposure Accelerates Development of Metabolic Syndrome among Middle-Aged Female Employees: A Five-Year Follow-Up

Abstract: Limited follow-up studies are available as to whether special job-types, such as day-night rotating shift work, contribute to the progression of metabolic syndrome among female industrial employees. A retrospective cohort study on the development of metabolic syndrome was conducted by utilizing health examination records for a five-year interval. The records of 387 female employees without metabolic syndrome at baseline were used for the analysis. Data analyzed included age, metabolic syndrome components, insulin resistance status, lifestyle factors, and job-types. The initial mean age of subjects was 32.8 yrs. Abnormal rates at baseline, including metabolic syndrome components and insulin resistance, were all significantly higher among the 34 female workers with metabolic syndrome outcome. Also, the persistent rotating shift-work exposure rates and five-year change of metabolic syndrome component measurements were significantly unfavorable for subjects with metabolic syndrome outcome. After controlling f...

Assessment of Chronotype in Four- to Eleven-Year-Old Children: Reliability and Validity of the Children's ChronoType Questionnaire (CCTQ)

Abstract: Individual differences in circadian phase preference ("chronotype") are linked to sleep schedule variability, psychosocial functioning, and specific properties of the circadian clock. While much is known about the development, distribution, and variability of chronotype in adolescents and adults, assessment in prepubertal children has been hindered by a lack of appropriate, reliable, and valid measures. This study presents a detailed description of the assessment of children's chronotype by the Children's ChronoType Questionnaire (CCTQ). The CCTQ is a parent-report, 27-item mixed-format questionnaire resulting in multiple measures of chronotype in 4- to 11-yr-old children: the midsleep point on free days (MSF), a morningness/eveningness scale (M/E) score, and a five-point chronotype (CT) score. The study provides validity data using actigraphy as well as test-retest reliability data for all three chronotype measures and sleep/wake parameters. Overall, the findings indicate moderate to strong agreement between the three measures, adequate associations between chronotype measures and sleep/wake parameters assessed by actigraphy, and excellent temporal stability (reliability).

Sleep quality in professional ballet dancers.

Abstract: Ballet dancers are competitive athletes who undergo extreme physical and mental stress and work according to an irregular schedule, with long days of training, rehearsal, and performance. Their most significant potential risks entail physical injury and altered sleep. The elaborate training requirements for ballet dancers do not allow regular chronobiological patterns or a normal sleep-wake rhythm. Our aim was to investigate the sleep-wake rhythm and sleep quality during rehearsal phases prior to a ballet premiere. We used wrist actigraphy and sleep diaries for a period of 67 days before the ballet premiere performance to study 24 classical ballet dancers. We likewise applied the Epworth Sleepiness Score (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-12 Quality of life Assessment, and d2 Test of Attention to assess quality of sleep, aspects of cognitive performance, and health status. We found significant reduction in sleep duration, from 418+/-43 min to 391+/-42 min, and sleep efficiency, from 81+/-4% to 79+/-5%, over the 67-day course of the rehearsal. We also found a decline in time in bed and an increase in wakefulness after sleep onset. Sleep onset latency did not change. However, the changes in sleep as documented by actigraphy were not reflected by the subjective data of the sleep diaries and sleep scores. As a result of the facts that total sleep efficiency and sleep duration values were already lower than usual for the dancers' age group at the beginning of the study and that mental acuity, concentration, and speed were likewise impaired, we observed exacerbated health deterioration in terms of sleep deprivation in ballet dancers during preparation for a premier. We conclude that individual activity-rest schedules, including daytime naps, may be helpful, especially during the stressful training and rehearsal experienced prior to ballet premieres.

The circadian clock gene Per1 suppresses cancer cell proliferation and tumor growth at specific times of day.

Abstract: Cell cycle progression is tightly regulated. The expressions of cell cycle regulators, the products of which either promote or inhibit cell proliferation, oscillate during each cell cycle. Cellular proliferation and the expression of cell cycle regulators are also controlled by the circadian clock. Disruption of the circadian clock may thereby lead to deregulated cell proliferation. Mammalian Per2 is a core clock gene, the product of which suppresses cancer cell proliferation and tumor growth in vivo and in vitro. Because Per1, another key clock gene, is mutated in human breast cancers, and because its clock functions are similar and complementary to those of Per2, we have studied its role in modulating breast cancer cell proliferation and tumor growth. We find that breast cancer growth rate is gated by the circadian clock with two daily peaks and troughs, and that they are coupled to the daily expression patterns of clock-controlled genes that regulate cell proliferation. Down-regulation of the expressio...

Blue light exposure reduces objective measures of sleepiness during prolonged nighttime performance testing.

Abstract: This study examined the effects of nocturnal exposure to dim, narrowband blue light (460 nm, approximately 1 lux, 2 microW/cm2), compared to dim broad spectrum (white) ambient light ( approximately 0.2 lux, 0.5 microW/cm2), on subjective and objective indices of sleepiness during prolonged nighttime performance testing. Participants were also exposed to a red light (640 nm, approximately 1 lux, 0.7 microW/cm2) placebo condition. Outcome measures were driving simulator and psychomotor vigilance task (PVT) performance, subjective sleepiness, salivary melatonin, and electroencephalographic (EEG) activity. The study had a repeated-measures design, with three counterbalanced light conditions and a four-week washout period between each condition. Participants (n = 8) maintained a regular sleep-wake schedule for 14 days prior to the approximately 14 h laboratory study, which consisted of habituation to light conditions followed by neurobehavioral performance testing from 21:00 to 08:30 h under modified constant-routine conditions. A neurobehavioral test battery (2.5 h) was presented four times between 21:00 and 08:30 h, with a 30 min break between each. From 23:30 to 05:30 h, participants were exposed to blue or red light, or remained in ambient conditions. Compared to ambient light exposure, blue light exposure suppressed EEG slow wave delta (1.0-4.5 Hz) and theta (4.5-8 Hz) activity and reduced the incidence of slow eye movements. PVT reaction times were significantly faster in the blue light condition, but driving simulator measures, subjective sleepiness, and salivary melatonin levels were not significantly affected by blue light. Red light exposure, as compared to ambient light exposure, reduced the incidence of slow eye movements. The results demonstrate that low-intensity, blue light exposure can promote alertness, as measured by some of the objective indices used in this study, during prolonged nighttime performance testing. Low intensity, blue light exposure has the potential to be applied to situations where it is desirable to increase alertness but not practical or appropriate to use bright light, such as certain occupational settings.

Daily and seasonal variation in the spectral composition of light exposure in humans.

Abstract: Light is considered the most potent synchronizer of the human circadian system and exerts many other non-image-forming effects, including those that affect brain function. These effects are mediated in part by intrinsically photosensitive retinal ganglion cells that express the photopigment melanopsin. The spectral sensitivity of melanopsin is greatest for blue light at approximately 480 nm. At present, there is little information on how the spectral composition of light to which people are exposed varies over the 24 h period and across seasons. Twenty-two subjects, aged 22+/-4 yrs (mean+/-SD) participated during the winter months (November-February), and 12 subjects aged 25+/-3 yrs participated during the summer months (April-August). Subjects wore Actiwatch-RGB monitors, as well as Actiwatch-L monitors, for seven consecutive days while living in England. These monitors measured activity and light exposure in the red, green, and blue spectral regions, in addition to broad-spectrum white light, with a 2 min resolution. Light exposure during the day was analyzed for the interval between 09:00 and 21:00 h. The time course of white-light exposure differed significantly between seasons (p = 0.0022), with light exposure increasing in the morning hours and declining in the afternoon hours, and with a more prominent decline in the winter. Overall light exposure was significantly higher in summer than winter (p = 0.0002). Seasonal differences in the relative contribution of blue-light exposure to overall light exposure were also observed (p = 0.0006), in particular during the evening hours. During the summer evenings (17:00-21:00 h), the relative contribution of blue light was significantly higher (p < 0.0001) (40.2+/-1.1%) than during winter evenings (26.6+/-0.9%). The present data show that in addition to overall light exposure, the spectral composition of light exposure varies over the day and with season.

Clock Genes Display Rhythmic Expression in Human Hearts

Abstract: Thus far, clock genes in the heart have been described only in rodents, and alterations of these genes have been associated with various myocardial malfunctions. In this study, we analyzed the expression of clock genes in human hearts. Left papillary muscles of 16 patients with coronary heart disease, 39 subjects with cardiomyopathy, and 9 healthy donors (52 males and 12 females, mean age 55.7+/-11.2; 16-70 yrs) were obtained during orthotopic heart transplantation. We assessed the mRNA levels of PER1, PER2, BMAL1, and CRY1 by real time PCR and analyzed their rhythmic expression by sliding means and Cosinor functions. Furthermore, we sought for differences between the three groups (by ANOVAs) for both the total 24 h period and separate time bins. All four clock genes were expressed in human hearts. The acrophases (circadian rhythm peak time) of the PER mRNAs occurred in the morning (PER1: 07:44 h [peak level 187% higher than trough, p = .008]; PER2: 09:42 h [peak 254% higher than trough, p < .0001], and BMAL1 mRNA in the evening at 21:44 h [peak 438% higher than trough; p < .0001]. No differences were found in the rhythmic patterns between the three groups. No circadian rhythm was detected in CRY1 mRNA in any group. PER1, PER2, and BMAL1 mRNAs revealed clear circadian rhythms in the human heart, with their staging being in antiphase to those in rodents. The circadian amplitudes of the mRNA clock gene levels in heart tissue are more distinct than in any other human tissue so far investigated. The acrophase of the myocardial PER mRNAs and the trough of the myocardial BMAL1 coincide to the time of day of most frequent myocardial incidents.

Amber lenses to block blue light and improve sleep: a randomized trial

Abstract: All light is not equal: blue wavelengths are the most potent portion of the visible electromagnetic spectrum for circadian regulation. Therefore, blocking blue light could create a form of physiologic darkness. Because the timing and quantity of light and darkness both affect sleep, evening use of amber lenses to block blue light might affect sleep quality. Mood is also affected by light and sleep; therefore, mood might be affected by blue light blockade. In this study, 20 adult volunteers were randomized to wear either blue-blocking (amber) or yellow-tinted (blocking ultraviolet only) safety glasses for 3 h prior to sleep. Participants completed sleep diaries during a one-week baseline assessment and two weeks' use of glasses. Outcome measures were subjective: change in overall sleep quality and positive/negative affect. Results demonstrated that sleep quality at study outset was poorer in the amber lens than the control group. Two- by three-way ANOVA revealed significant (p < .001) interaction between q...

Diurnal variation in endotoxin-induced mortality in mice: correlation with proinflammatory factors.

Abstract: Many immune parameters exhibit daily and circadian oscillations, including the number of circulating cells and levels of cytokines in the blood. Mice also have a differential susceptibility to lipopolysaccharide (LPS or endotoxin)-induced endotoxic shock, depending on the administration time in the 24 h light-dark (LD) cycle. We replicated these results in LD, but we did not find temporal differences in LPS-induced mortality in constant darkness (DD). Animals challenged with LPS showed only transient effects on their wheel locomotor activity rhythm without modification of circadian period and phase. Levels of several key factors involved in the pathology of sepsis and septic shock were tested in LD. We found that LPS-induced levels of interleukin (IL)-1beta, IL-6, JE (MCP-1), and MIP1alpha were significantly higher at zeitgeber time (ZT) 11 (time of increased mortality) than at ZT19 (ZT12 = time of lights-off in the animal quarters for the 12L:12D condition). Our results indicate that the differences found in mortality that are dependent on the time of LPS-challenge are not directly related to an endogenous circadian clock, and that some relevant immune factors in the development of sepsis are highly induced at ZT11, the time of higher LPS-induced mortality, compared to ZT19.

Phase Delaying the Human Circadian Clock with Blue-Enriched Polychromatic Light

Abstract: The human circadian system is maximally sensitive to short-wavelength (blue) light. In a previous study we found no difference between the magnitude of phase advances produced by bright white versu...

Shiftwork and impaired glucose metabolism: a 14-year cohort study on 7104 male workers.

Abstract: The aim of this study was to assess the effect of shiftwork on hemoglobin A1c (HbA1c) level, as an index of glucose metabolism. A 14 yr prospective cohort study was conducted on day (n = 4219) and alternating shiftworkers (n = 2885) who received annual health checkups between 1991 and 2005 at a Japanese steel company. The endpoints were either a 10%, 15%, 20%, 25%, or 30% increase in HbA1c during the period of observation, compared to HbA1c at entry to the study. The association between the type of job schedule and increase in HbA1c was investigated after adjusting for age, body mass index, mean arterial pressure, total serum cholesterol, creatinine, alanine aminotransferase, gamma-glutamyl transpeptidase, uric acid, drinking habit, smoking habit, and habitual exercise using multivariate pooled logistic regression analyses. Shiftwork was significantly associated with the various HbA1c endpoints (> or =10% HbA1c increase, odds ratio 1.35 [95% confidence interval 1.26-1.44]; > or =15% HbA1c increase, odds ratio 1.29 [95% confidence interval, 1.19-1.40]; > or =20% HbA1c increase, odds ratio 1.23 [95% confidence interval 1.11-1.37]; and > or =25% HbA1c increase, odds ratio 1.19 [95% confidence interval 1.03-1.36]). Age, body mass index, alanine aminotransferase, and gamma-glutamyl transpeptidase were associated positively with all five HbA1c endpoints. Uric acid was associated negatively with all five HbA1c endpoints. Our study on male Japanese workers revealed alternating shiftwork (in addition to other established factors, such as age and body mass index) was a consistent risk factor for impaired glucose metabolism.

Phase angle of entrainment in morning- and evening-types under naturalistic conditions.

Abstract: Differences in morningness-eveningness among humans are commonly ascribed to circadian parameters, such as circadian period and responsivity to environmental time cues, as well as homeostatic sleep drive. Light is the primary synchronizer of the human biological clock, and if circadian differences exist between morning and evening types, they should have different phase angles of entrainment to the light/dark cycle; that is, morning and evening types should have different patterns of light exposure relative to endogenous circadian phase (ECP). When phase angle of entrainment is strictly defined as the relationship between a marker of ECP and the timing of light exposure, such differences have been demonstrated in the laboratory under controlled light/dark cycles and have recently been shown under conditions of spring and summer light exposure outside the laboratory, taking into account the variable intensity of light. Here, we report similar results from a large (n = 66), diverse cohort of morning and evening types across the age span studied at all different times of the year. Differences between morning and evening types in light exposure relative to ECP, indicative of a difference in the phase angle of entrainment to the external light/dark cycle, were found. Specifically, evening types, compared to morning types, had a higher ratio of phase advancing to phase delaying by light. We interpret this as indicating a longer circadian period (τ) in evening types.

Light intensity exposure, sleep duration, physical activity, and biomarkers of melatonin among rotating shift nurses.

Abstract: Long-term, night shiftwork has been identified as a potential carcinogenic risk factor. It is hypothesized that increased light at night exposure during shiftwork reduces melatonin production, which is associated with increased cancer risk. Sleep duration has been hypothesized to influence both melatonin levels and cancer risk, and it has been suggested that sleep duration could be used as a proxy for melatonin production. Finally, physical activity has been shown to reduce cancer risk, and laboratory studies indicate it may influence melatonin levels. A cross-sectional study of light exposure, sleep duration, physical activity, and melatonin levels was conducted among 61 female rotating shift nurses (work schedule: two 12 h days, two 12 h nights, five days off). Light intensity was measured using a light-intensity data logger, and sleep duration and physical activity were self-reported in a study diary and questionnaire. Melatonin concentrations were measured from urine and saliva samples. The characteri...

In Sync with the Family: Children and Partners Influence the Sleep‐Wake Circadian Rhythm and Social Habits of Women

Abstract: Different factors have been proposed to influence morningness‐eveningness, biological rhythms, and sleep‐wake cycles, but few studies focused on the influence of social habits Here, we focus on the influence of children and partners on the social habits of women at different stages of their lives and on synchronization within the family One hundred and seventy‐nine women participated in the study and were allocated into four groups: women without children, pregnant women without children, pregnant women with children, and non‐pregnant mothers Morningness was predicted by the presence of children, and earlier chronotype was predicted by the presence of children, pregnancy, and age Average sleep duration was longest in pregnant women The presence of children was responsible for a difference in rise times of approximately 15 h on the weekend Subjective sleep‐onset latencies were shortest in women with children The synchrony between partners (husband/wife) was 046 in women without children, 079 in p

Administration-time-dependent effects of olmesartan on the ambulatory blood pressure of essential hypertension patients.

Abstract: Previous studies established that a single daily dose of olmesartan remains effective for the entire 24 h without alteration of the day-night blood pressure (BP) pattern. On the other hand, the administration of valsartan or telmisartan at bedtime, as opposed to upon wakening, improves the sleep-time relative BP decline toward a greater dipper pattern without loss of 24 h efficacy. Yet to be determined is whether this administration-time-dependent efficacy is a class-related feature, characteristic of all angiotensin-receptor-blocker (ARB) medications. We studied 123 grade 1 and 2 hypertensive patients, 46.6+/-12.3 yrs of age, randomly assigned to receive olmesartan (20 mg/day) as a monotherapy either upon awakening or at bedtime for three months. BP was measured by ambulatory monitoring for 48 consecutive hours before and after treatment. The 24 h BP reduction was similar for both treatment times. Administration of olmesartan at bedtime, however, was significantly more efficient than morning administration in reducing the nocturnal BP mean. The sleep-time relative BP decline was slightly reduced with olmesartan ingestion upon awakening but significantly increased with ingestion at bedtime, thus reducing the prevalence of non-dipping from baseline by 48%. Olmesartan administration at bedtime, as opposed to in the morning, improved the awake/asleep BP ratio toward a greater dipper pattern without loss of 24 h efficacy. Nocturnal BP regulation was significantly better achieved with bedtime as compared to morning dosing of olmesartan. These effects are comparable to those previously reported for valsartan and telmisartan, thus suggesting that they may be class-related features of ARB medications in spite of differences in their half-life kinetics. These administration-time-dependent effects should be taken into account when prescribing ARB medications for treatment of essential hypertension.

Effects of one night of partial sleep deprivation upon diurnal rhythms of accuracy and consistency in throwing darts.

Abstract: Sixty subjects were tested five times per waking day on two occasions for accuracy and reliability in throwing 20 darts at a target. Two experimental conditions were investigated: following a normal nocturnal sleep (7-8 h sleep, normal) and after having retired to bed 4 h later than normal the previous night but rising at the normal time (3-4 h sleep, sleep deprivation). Sublingual (core) temperature and subjective estimates of alertness and fatigue were measured in all sessions. Performance at throwing darts was assessed by three methods: mean distance of the dart from the bulls-eye; number of times the target was missed; and variability of the scores from the darts thrown. There was no evidence that performance was affected by physical fatigue arising during the course of throwing the 20 darts. All variables showed significant diurnal rhythms, those of alertness and performance being phased over 1 h earlier than core temperature, and that of fatigue over 1 h earlier than the inverse of temperature. Core temperature was not affected by sleep deprivation, but all other variables showed significant changes, indicative of mood and performance decrement. Increasing time awake was associated with decreased alertness and increased fatigue, as well as slight negative effects upon performance. We conclude that the simple task of throwing darts at a target provides information about chronobiological changes in circumstances where time awake and sleep loss might affect psychomotor performance.

The food-entrainable oscillator: a network of interconnected brain structures entrained by humoral signals?

Abstract: Food is critical for all animal species. Its temporal availability is a relevant signal for organizing behavioral and physiological parameters. When food is restricted to a few hours per day, rats, mice, and other mammals exhibit anticipatory activity before mealtime (food-anticipatory activity). There is considerable evidence suggesting that this anticipation is mediated by a food-entrainable oscillator (FEO) with circadian properties, but located outside the suprachiasmatic nucleus of the hypothalamus (the light-entrainable oscillator). However, the locus of the FEO as well as the mechanisms by which food entrainment occurs is unclear. In this review, we summarize data about the potential input pathways to the FEO and propose a model for understanding it as a network of interconnected brain structures entrained by fluctuation of different humoral signals.

Morningness-eveningness, sex, and the alternative five factor model of personality

Abstract: Recent research on personality and circadian typology indicates that evening-type subjects are more extraverted, impulsive, and novelty-seeking, while morning ones tend to be more introverted, conscientious, agreeable, and emotionally stable. The purpose of this study was to examine the differences between circadian typologies on the Zuckerman's Alternative Five Factor Model of personality (AFFM), which has a strong biological basis, controlling for sex and age. A sample of 533 university students (168 men) participated in the study. Results showed that morning-type subjects had significant higher scores than evening-type and neither-type subjects in Activity, and in its subscales General Activity and Work Activity. A significant interaction between circadian typology and sex was found for Neuroticism-Anxiety: morning-type men showed higher scores than evening-type and neither-type, who had the lowest scores. Women presented the opposite pattern: neither-type obtained the highest scores, while morning-type showed the lowest. This is the first time the AFFM has been used in the context of circadian rhythms research. The results suggest that activity is the only trait related to extraversion associated with morningness, while Neuroticism-Anxiety was modulated by sex. These results might help highlight previous results on the association between morningness-eveningness and other models of personality assessment, and they offer new data that calls for further research.

Time-of-day effects on fatigue during a sustained anaerobic test in well-trained cyclists.

Abstract: The aim of this study was to evaluate time-of-day effects on fatigue during a sustained anaerobic cycling exercise. Sixteen healthy male competitive cyclists were asked to perform a 60 s Wingate test against a braking load of 0.087 kg.kg body mass(-1) during two experimental sessions, which were set up either at 06:00 or 18:00 h in counterbalanced order. There was only one session per day with a recovery period of at least 36 h between the two sessions. Each subject was trained to perform the test. The body mass used to determine the braking load was that of the first test session for each subject and remained constant throughout the two test periods. During the test, peak power (PP), mean power during the first 30 s (MP30 s) and the full 60 s of the test (MP60 s), and fatigue (i.e., the decrease in power output values throughout the exercise) were analyzed. Results confirmed the existence of diurnal variation in anaerobic power output. PP, MP30 s, and MP60 s were significantly higher at 18:00 than 06:00 h, with gains equal to 8.2, 7.8, and 7.8%, respectively. Moreover, all the power output values recorded in the evening were higher than those recorded in the morning, indicating that fatigue induced by this exercise is not affected by time-of-day in male competitive cyclists. It is hypothesized that the freedom and complexity of pedalling could allow adaptations in movement patterns, as a function of time-of-day, in order to maintain higher performance in the evening. For practical considerations, the more complex the movements required to perform a sport, the more the time-of-day effect can be taken into account and adapted to by the trained athlete, particularly in cyclic sporting disciplines such as swimming, running, rowing, and kayaking.

Is light-at-night a health risk factor or a health risk predictor?

Abstract: In 2007, the IARC (WHO) has classified "shift-work that involves circadian disruption" as potentially carcinogenic. Ample evidence leaves no doubt that shift-work is detrimental for health, but the mechanisms behind this effect are not well understood. The hormone melatonin is often considered to be a causal link between night shift and tumor development. The underlying "light-at-night" (LAN) hypothesis is based on the following chain of arguments: melatonin is a hormone produced under the control of the circadian clock at night, and its synthesis can be suppressed by light; as an indolamine, it potentially acts as a scavenger of oxygen radicals, which in turn can damage DNA, which in turn can cause cancer. Although there is no experimental evidence that LAN is at the basis of increased cancer rates in shiftworkers, the scenario "light at night can cause cancer" influences research, medicine, the lighting industry and (via the media) also the general public, well beyond shiftwork. It is even suggested that baby-lights, TVs, computers, streetlights, moonlight, emergency lights, or any so-called "light pollution" by urban developments cause cancer via the mechanisms proposed by the LAN hypothesis. Our commentary addresses the growing concern surrounding light pollution. We revisit the arguments of the LAN theory and put them into perspective regarding circadian physiology, physical likelihood (e.g., what intensities reach the retina), and potential risks, specifically in non-shiftworkers.

Post-exercise blood pressure reduction is greater following intermittent than continuous exercise and is influenced less by diurnal variation.

Abstract: Recently, we reported that circadian variation exists in the response of blood pressure (BP) following a bout of uninterrupted exercise. The usual phenomenon of post‐exercise hypotension was absent or reversed when such exercise was performed between 04:00–08:00 h. Nevertheless, research examining BP changes following bouts of intermittent exercise at different times of the day is scarce, even though this type of activity is probably more popular. Therefore, we aimed to compare post‐exercise BP reductions of continuous (CONT) and intermittent (INT) exercise protocols performed at 08:00 h and 16:00 h. At both of these times of day, eight normotensive males completed 30 min of continuous cycling in the CONT and three 10 min bouts of cycling separated by 10 min of rest in the INT protocol. The exercise intensity was set at 70% V˙O2peak during both protocols. Heart rate, systolic (S) and diastolic (D) BP, and mean arterial pressure (MAP) were measured 5 min before and 20 min after exercise. Changes from pre‐e...

Seasonal variations in clock-gene expression in Atlantic salmon (Salmo salar).

Abstract: In homeothermic vertebrates inhabiting temperate latitudes, it is clear that the seasonal changes in daylength are decoded by the master circadian clock, which through secondary messengers (like pineal melatonin secretion) entrains rhythmic physiology to local conditions. In contrast, the entrainment and neuroendocrine regulation of rhythmic physiology in temperate teleosts is not as clear, primarily due to the lack of understanding of the clock gene system in these species. In this study, we analyzed the diel expression of the clock‐genes in brains of Atlantic salmon, a species that is both highly photoperiodic and displays robust clock‐controlled behavior. Atlantic salmon parr were acclimated to either long‐day (LD) or short‐day (SD) photoperiods for one month and thereafter sampled at 4 h intervals over a 24 h cycle. Clock, Bmal1, Per2, and Cry2 were all actively expressed in salmon brain homogenates and, with the exception of Per2, all displayed rhythmic expression under SD photoperiods that parallels...

Synchronization to light and restricted-feeding schedules of behavioral and humoral daily rhythms in gilthead sea bream (sparus aurata)

Abstract: Food is not continuously available in the wild, and so most animals show a wide variety of circadian rhythms that can be entrained to feeding time. The aim of this research was to evaluate the effect of time-restricted feeding on the daily rhythms of gilthead sea bream, with food being provided during the day or night under a 12:12 h light-dark (LD) cycle or constant light (LL) conditions. Self-feeding and locomotor activity, as well as daily rhythms of cortisol, glucose, and melatonin, were evaluated. Fish synchronized their feeding behavior to the feeding phase, so that in LD they displayed 78% nocturnal feeding activity under night-feeding and 81% diurnal feeding activity under day-feeding, while under LL-feeding they displayed 72% of their daily activity during the 12 h feeding phase. In contrast, locomotor activity was mostly diurnal (66–71%), regardless of the feeding schedule, and it became arrhythmic under LL. Cortisol showed daily rhythms that peaked at different times, depending on the light and...

Discoveries of rhythms in human biological functions: a historical review.

Abstract: Though there are very early and ancient observations on the daily variation in physiological and pathophysiological functions (e.g., bronchial asthma), more detailed and scientific reports were not published until the beginning of the 17th century. The aim of this review is to bring those reports to the attention of researchers of chronobiology and chronopharmacology. The ancient books and their contents, which constitute the basis for this review, are part of the personal library collection of the author; numerous observations and reports on biologic rhythms in man are presented here for the first time. The intent of this review is to demonstrate that the fields of chronobiology and chronopharmacology are not only a new and modern branch of science, but that it stands on the shoulders of wonderful and insightful observations and explanations made by our scientific forefathers. It is the hope that the reader will enjoy the richness of the ancient reports that contribute to our present knowledge achieved through astute early biologic rhythm research.

Circadian rhythmicity in murine pre-adipocyte and adipocyte cells

Abstract: Adipose tissue is central to metabolic homeostasis, signaling in part through the secretion of molecules termed adipokines. Circadian rhythms play an important role in adipose physiology, with plasma adipokine concentration and approximately 20 % of the murine adipose transcriptome undergoing 24 h variation. However, due to the heterogeneity of adipose tissue and rhythmical input from both neuronal and humoral signals, the cellular basis of adipose rhythms is unclear. We tested the hypothesis that adipocyte cells contain a circadian clock that drives rhythmic mRNA expression and adipokine secretion. From the murine pre-adipocyte 3T3-L1 cell line, we generated populations of both pre-adipocytes and differentiated adipocytes. Cells were then treated with a 2 h serum pulse and sampled every 4 h over a 48 h period. Expression of clock gene, 'metabolic' gene (PPARalpha, PPARgamma, SREBP1), and adipokine mRNA was analyzed by quantitative real-time PCR, and secretion of the adipokines leptin and adiponectin was measured in culture medium from differentiated adipocytes. In pre-adipocytes, we observed robust rhythms of clock genes Per2, Rev-erbalpha, and Dbp, but not of Per1, Cry1, Bmal1, or any of the 'metabolic' genes. Adipocytes produced similar temporal profiles of mRNA expression, albeit with a markedly reduced amplitude of Per2 and Dbp rhythms. Despite no circadian rhythm of adipokine mRNA expression, leptin accumulation in the culture medium suggested circadian control of leptin secretion from adipocytes. Adiponectin secretion showed temporal variation, but without any apparent circadian rhythmicity. Our data, therefore, suggest that an endogenous adipocyte clock controls the rhythmic expression of only a subset of genes that are reported to exhibit 24 h rhythmicity in murine adipose tissue. Moreover, secretion of leptin may also be regulated by the adipocyte clock.

The nocturnal activity of fruit flies exposed to artificial moonlight is partly caused by direct light effects on the activity level that bypass the endogenous clock.

Abstract: Artificial moonlight was recently shown to shift the endogenous clock of fruit flies and make them nocturnal To test whether this nocturnal activity is partly due to masking effects of light, we exposed the clock-mutants per(01), tim(01), per(01);tim(01), cyc(01), and Clk(JRK) to light/dark and light/dim-light cycles and determined the activity level during the day and night We found that under moonlit nights, all clock mutants shifted their activity significantly into the night, suggesting that this effect is independent of the clock We also recorded the flies under continuous artificial moonlight and darkness to judge the effect of dim constant light on the activity level All mutants, except Clk(JRK) flies, were significantly more active under artificial moonlight conditions than under complete darkness Unexpectedly, we found residual rhythmicity of per(01) and especially tim(01) mutants under these conditions, suggesting that TIM and especially PER retained some activity in the absence of its respective partner Nevertheless, as even the double mutants and the cyc(01) and Clk(JRK) mutants shifted their activity into the night, we conclude that dim light stimulates the activity of fruit flies in a clock-independent manner Thus, nocturnal light has a twofold influence on flies: it shifts the circadian clock, and it increases nocturnal activity independently of the clock The latter was also observed in some primates by others and might therefore be of a more general validity